One fraud method commonly used in payment terminals authorizing payment by coins consists of attaching the coin to one end of a thread, before inserting it into the payment terminal using the insertion slot provided for that purpose. The coin attached to the end of the thread then enters the money selector and falls into the pre-collection bucket. When the transaction is validated, the bucket moves to its payment position, in which the coins it contains are normally discharged toward the moneybox under the effect of gravity. However, the coin in question being attached to the end of a thread whereof the opposite end is held by the perpetrator of the fraud, it cannot be discharged toward the moneybox and remains in the bucket. The perpetrator of the fraud then performs a second transaction, during which he inserts the new coin and releases the thread. The coin newly inserted, as well as the coin attached to his thread, fall onto the bottom of the bucket. The perpetrator of the fraud then cancels the transaction so that the bucket moves to its coin return position and discharges the two coins to the bowl, where they are recovered by the perpetrator of the fraud.
This fraud system thus allows the perpetrator to obtain parking authorization at no cost for a length of time corresponding to the amount of the first inserted coin.
It is possible to detect such fraud by providing optomechanical sensors in the payment terminals, those sensors being capable of detecting the presence of the thread. However, such a detection system is not fully satisfactory. In fact, its effectiveness is limited to rigid and/or tensioned threads.
It is also possible to add flaps at the slot for inserting coins into the payment terminal. These flaps are designed to prevent a thread from being passed into the slot. Such an anti-fraud system is also not fully satisfactory. Indeed, it is visible and accessible from outside the terminal, which makes it easier for a person intending to commit fraud to bypass or neutralize.